btn.addEventListener('click', downloadFile); ); The PDF may be > 20 MB. Using response.blob() after the full download is still streamed internally, but the code above keeps it simple. If you need true progressive streaming (e.g., showing a progress bar), replace the blob() call with the ReadableStream ‑based approach shown in the Advanced section at the end. 2️⃣ Back‑End – Flask API Endpoint Below is a minimal, secure, and testable Flask service that delivers the PDF. NOTE: If the PDF is copyrighted and not publicly licensed, you must enforce authentication or access‑control before serving it. The example includes a placeholder @login_required decorator you can swap for Flask‑Login, JWT, or any custom logic. 2.1 Project Layout project/ │ ├─ app/ │ ├─ __init__.py │ ├─ routes.py │ └─ utils.py │ ├─ static/ │ └─ pdf/ │ └─ GR-3108-Core.pdf ← (keep this outside public static!) │ ├─ requirements.txt └─ run.py 2.2 requirements.txt Flask==3.0.3 gunicorn==22.0.0 Werkzeug==3.0.3 (Add Flask-Login or PyJWT if you need auth.) 2.3 app/ init .py from flask import Flask from .routes import bp as api_bp
bp = Blueprint("download", __name__)
# `as_attachment=True` forces the Content‑Disposition header. response = send_file( path, mimetype="application/pdf", as_attachment=True, download_name=filename, conditional=True # enables Range support ) response = add_download_headers(response, filename) gr 3108 core pdf download
# 2️⃣ Test locally python run.py # → http://localhost:5000/api/v1/download/gr-3108-core 2️⃣ Back‑End – Flask API Endpoint Below is